The present invention relates to an apparatus for machining by electrical discharges an electrode workpiece by means of an electrode tool, the electrodes being displaced relative to each other along a feed axis of the electrode tool within the workpiece and in a plane perpendicular to the feed axis.
It is known in EDM technology that imparting a translation motion to one of the electrodes in a plane perpendicular to the feed axis of the electrode tool relative to the electrode workpiece presents the advantage of obtaining a controlled quasi-enlargement of the transverse section of the electrode tool during its feed into the workpiece.
Devices for achieving such results are disclosed in U.S. Pat. Nos. 3,539,754 and 3,809,852, which further disclose means for progressively varying the amplitude of the translation motion as a function of the amount of penetration of the electrode tool within the workpiece, such as to provide the surface of a cavity in the workpiece with a predetermined taper. Another known machining method consists in varying the amount of eccentricity of the translation motion in the same ratio as the relative displacement of the electrodes along the feed axis. By such a method, a three-dimensional expansion of the electrode tool is obtained together with a simultaneous control of the axial and radial feeds.
Because they provide a relative feed of the electrodes always comprising an axial component, those prior art apparatus and methods do not permit to effectuate a machining of the electrode workpiece exclusively in a radial direction, for example, for machining a groove, by means of an electrode tool in the form of a disc, in the lateral surface of a cavity in the electrode workpiece.
The apparatus of the invention has for principal object to provide an arrangement permitting to transform a three-dimensional machining operation into a controlled radial machining operation. The apparatus of the invention further presents the advantage of being adaptable to all the prior art apparatus wherein the amount of eccentricity of radial displacement of an electrode varies as a function of the axial relative displacement of the electrode tool and the electrode workpiece. The invention provides a simple and economical fixture for modifying the axial component of the relative translation motion of the electrodes during three-dimensional EDM machining, such as to change the path of the translation motion to provide the workpiece with a predetermined shape.